LABORATORY STUDIES AND DEMONSTRATIONS. 207 



surface (stained witli dilute iodine to sliow nnolei and ^itarcli- 

 grains), and frou-'s or newt's l>lood, mixed with nuniial salt scJu- 

 tion, and examined either fresh or slightly stained with dilute 

 iodine. 



Thin sections of pith (elder, etc.), from which the air lias 

 been displaced by alcohol, give good pictures of tissue c<>jn]>used 

 of empty cells. Fresh or alcoholic nniscle from the frog's leg, 

 gently teased out, shows muscular tissue to be composed of elon- 

 gated cells (iihres). Finally, the student may prove that he 

 Inmself is composed of cells by gently scraping the inside of his 

 lip or cheek with a scalpel, mounting the scrapings on a slide, 

 and after adding a drop of Delalield's h^ematoxylin, covering, 

 and examining in the usual way. 



To show the lifeless matter in living tissue it suffices to ex- 

 amine frog's blood or human blood; sections of potatoes, es- 

 pecially if lightly stained wdth iodine ; sections of geranium stems. 

 {Pelargonium)^ which usually show crystals in some of the more 

 peripheral cells ; cartilage, stained with iodine, in which the life- 

 less matrix remains uncolored ; or prepared sections of bone, in 

 which the spaces once filled by the living cells are now black and 

 opaque, being filled with dust in the grinding, or with air. 



Chapter III. (Protoplasm and the Cell.) 



Naked-eye Examination of Protoplasm. A drop of ]u'oto- 

 plasm is readily obtained from one of the long (internodal) cells 

 of Nitella^ after removing the superfluous water and snipping off 

 one end of the cell with scissors. The cell collapses and the 

 drop forms at the lower (cut) end. It may be transferred to a 

 (dry) slide and tested for its viscidity by touching it with a 

 needle. Microscopically it is instructive chiefly by its lack of 

 marked structure. 



The Parts of the Cell. The structure of the cell is beauti- 

 fully shown in properly stained and mounted preparations of un- 

 fertilized star-fish or sea-urchin eggs, or of apical buds of j^iUUa. 

 If these are not availal)le potato-cells or cartilage cells do very 

 well; or sections of epithelium, glands, etc., may be shown. 



The class may also mount and draw frog's or newt's blood- 

 cells, prepared and double-stained as follows. The blood is spread 



